The invention generally relates to devices and methods for applying a lubricating coating to one or more surfaces of metallic sheet materials such as, for example, tin-plated steel stock, and aluminum sheet stock used to make aluminum beverage cans.
Metallic sheet materials are used in the fabrication of a wide variety of articles of manufacture including beverage cans, metal housings, metal panels, metal tools, structural metal components, etc. Such metallic sheet materials are pressed, forged, stamped, drawn, ironed or otherwise formed using pressure applied in various ways to shape the metal sheet materials into useful products. In many such forming processes, it is essential that one or more surfaces of the metallic sheet materials are coated with one or more lubricant compositions of petroleum and vegetable oils, petroleum distillates, esters, fatty acids and other components that provide lubricating properties to metallic sheet surfaces.
In many manufacturing processes, the lubricant coatings are applied to the sheet surfaces as the sheet material moves through the forming process. The lubricants perform functions including the primary function of reducing the coefficient of friction between the metallic sheet surfaces and the surfaces of handling equipment, press components, forming dies and other related forming equipment. Thus, the proper application of lubricant coatings to the moving sheet surfaces is essential to such manufacturing processes and prevents substantial product defects, waste of materials, product failures, excessive forming and handling equipment wear, excess maintenance costs and other undesired adverse effects.
For example, such lubricant coatings are used in the process for forming tin-plated steel stock into various articles of manufacture, and for forming aluminum sheet stock into beverage can bodies. In forming aluminum stock into beverage can bodies, a continuous strip of aluminum sheet stock is fed from a supply coil to a xe2x80x9ccupping press.xe2x80x9d In that press, metal dies punch disks of aluminum from the sheet stock and press the disks into shallow cup-shaped blanks. The xe2x80x9ccupsxe2x80x9d are transferred to a xe2x80x9cbody makerxe2x80x9d where they are drawn and ironed into the shape of an elongated can body. The can body typically is trimmed and then cleaned, coated, printed and often subject to one or more additional shaping steps before it is filled with a beverage and sealed.
In the xe2x80x9ccupxe2x80x9d forming step, substantial frictional engagement occurs between the surfaces of the aluminum sheet stock and portions of the cupping press contacting the sheet stock surfaces, including the forming dies, stripping plates and other press surfaces. Consequently, one or more lubricating coatings are applied to the exposed upper and lower surfaces of the moving aluminum sheet stock while it is fed into the cupping press. The lubricating coating reduces the coefficient of friction at the interface surfaces of the aluminum sheet and the cupping press, and particularly the surfaces of the forming dies, to facilitate the proper pressing of the aluminum xe2x80x9ccupsxe2x80x9d The lubricant coating also assists in proper passage of the sheet material into the press and waste materials out of the press. Those waste materials include the remaining web of aluminum sheet after the xe2x80x9ccupsxe2x80x9d are punched from the aluminum sheet stock.
The inconsistent, inadequate, and non-uniform application of the lubricant coating to the moving aluminum sheet stock surfaces (as well as the surfaces of tin-plated steel and other metallic sheet materials) can result in under-lubrication of portions of the metallic sheet surfaces and, in some instances, over-lubrication of other portions of the sheet surfaces. As a result, excessive frictional forces may develop on the under-lubricated portions of the sheet surfaces at various stages of the forming process that interfere with or even prevent proper operation of the forming process. Inadequate lubrication of the sheet surfaces also may result in excessive defects in portions of the formed product, damage and excessive wear to the presses and forming dies, loss of materials and production time due to improperly formed products, increased press down time, sheet or product jams, increased costs of material and labor, and similar undesirable interruptions and inefficiencies in the manufacturing process.
For example, if an inadequate amount of lubricant coating is applied to the aluminum sheet metal used to make can bodies, then the aluminum xe2x80x9ccupsxe2x80x9d may not properly form during the cupping stage. The xe2x80x9ccupsxe2x80x9d may have holes or gaps in their sides or bottom, they may acquire undesirable draw marks or scratches on their sides and bottoms, they may have inconsistent dimensions or other such defects rendering them unacceptable for further processing. If such difficulties with the lubricant coatings persist, the defects rates, materials waste, and cost inefficiencies can quickly reach commercially unacceptable levels.
Similarly, the application of excessive amounts of lubricant to the sheet material surfaces also is undesirable. Over lubrication of part or all of the sheet material surfaces may result in inadequate forming pressures, sticking between press and sheet material surfaces, feed jams, improper forming, product ejection jams, jams in waste material ejection systems and other similar adverse effects. The use of excessive amounts of lubricants also may result in unwanted build up of lubricants on the forming and handling equipment requiring increased cleaning and maintenance cost and excessive lubricant expenses.
Thus, in most, if not all, applications it is desirable to apply such lubricant compositions to the sheet material surfaces in a generally uniform layer to ensure that the sheet surfaces are provided with a sufficient, but not excessive, amount of the lubricant composition. The amount of the lubricant composition and its distribution may vary from one manufacturing process to another depending on the composition of the metallic sheet materials, the surface properties and characteristics of the materials, the surface area exposed for contact with the handling and forming equipment, the size and shape of the formed product, and the forming conditions (pressures, temperatures, speeds, etc.), among other considerations that affect the necessary amount and distribution of the lubricant coating. In some applications, those amounts and distribution may be calculated, in others they are determined by field testing and analysis.
The careful control of the amount and application rate of a lubricant coating also provides substantial opportunities to optimize the necessary amount of lubricant applied and the distribution of the lubricant to enhance the operation of the forming and handling process and to minimize manufacturing expenses. Such improved controls and application methods also permit the consideration of improved forming processes, increased production speeds, alternative sheet material compositions, improved production schedules and desirable cost containment approaches.
Such improved controls are a concern in many forming processes, including aluminum can body forming processes where the sheet material feed rates are inconsistent and vary over short periods of time from relatively slow rates to relatively fast rates. Such improved controls are of particular concern where it is desirable to reduce or minimize the amount of lubricant applied to the metallic sheet surfaces. In that instance, even small variations in the lubricant coating as one approaches the minimum required lubricant amount may result in significant production difficulties due to the potential for inadequate lubrication of portions or all of the sheet material surfaces. The need for improved control over the application of the lubricant coating is further necessary where increased sheet feed rates are desired.
In prior conventional systems, a variety of approaches were used to apply and distribute the necessary lubricant coatings to sheet material surfaces. For example, in one system, a continuous length of metallic sheet material was immersed and advanced through a lubricant composition bath. A squeegee, blade or roller system then was used to remove the excess lubricating composition from the sheet surfaces and reduce the coating to the desired amount, thickness and distribution.
In those and other conventional systems, it often was difficult to maintain a consistent and uniform lubricant coating, particularly when using xe2x80x9cneatxe2x80x9d lubricant compositions comprised primarily of active lubricating components. In addition, it often was difficult to operate such conventional systems cost effectively at relatively high sheet feed rates, and at highly variable sheet feed rates, to avoid excessive waste of the lubricant composition and to reduce significant cost inefficiencies.
The active component of the lubricant compositions typically used in the production of aluminum beverage cans are petroleum oils, vegetable oils, esters, fatty acids, emulsifiers, surfactants and combinations thereof. The amount of the active lubricant component applied to aluminum sheet stock prior to the cupping operation typically can range from approximately 100 mg/M2 to approximately 400 mg/M2, which is equivalent to approximately about 10 to 45 mg/ft2, or about 6 to about 10 mg/gm of xe2x80x9ccupxe2x80x9d (where approximately 4 to 5 xe2x80x9ccupsxe2x80x9d are formed per square foot of sheet stock).
Conventional lubricating systems often cannot effectively provide coatings formed from such lubricant compositions in their xe2x80x9cneatxe2x80x9d form, particularly at the lower desired application amounts for many of the above-mentioned reasons. Moreover, attempts to reduce and optimize the amount of xe2x80x9cneatxe2x80x9d lubricant used to form the required coating have not overcome undesirable fluctuations in the amount, distribution and thickness of the coatings applied by such conventional systems in a commercially acceptable fashion.
As a consequence, one approach to address those difficulties was to modify the lubricant composition rather than the application system. For example, in many conventional systems, the active lubricant components are emulsified with water to form an aqueous lubricating composition. The composition of such lubricant emulsions typically include approximately from 40% to 75% water and approximately 25% to 60% active lubricants and emulsifiers. By using such aqueous emulsions, one could coat the sheet material with a desired amount of active lubricant by applying the emulsion in sufficiently large, more controllable volumes. As a result, the use of emulsified lubricant compositions permitted improved application of reduced amounts of active lubricant composition to the sheet surfaces, along with significant amounts of water.
However, the use of aqueous emulsions in such systems created other undesirable effects that impacted both the effective operation and the cost efficiency of metallic sheet forming processes, including those used to form the aluminum xe2x80x9ccupsxe2x80x9d for beverage can bodies. The presence of relatively large volumes of water in the prior lubricant emulsions often caused corrosion and increased wear on the metallic surfaces of the presses and forming dies. Aqueous lubricant emulsions, in addition, typically tended to leach important metallic components from the metal surfaces of the forming presses and forming die surfaces, such as cobalts and nickels, which are in regular contact with the aqueous lubricant emulsion. That corrosion, leaching and the resulting increased wear on the press and die surfaces impaired the proper operation of the presses over extended periods of time and reduced the expected useful life for the press components.
In addition, in many processes, the use of large amounts of aqueous emulsions required significant recycling systems to allow the conservation and reuse of excess lubricant emulsions. Such recycling systems increased the overall system expenses and maintenance requirements, and further require additional filters, pumps, and preservatives and other precautions to limit the risk of contamination and deleterious impurities in the emulsion.
For example, aqueous emulsions used in xe2x80x9ccuppingxe2x80x9d operations for forming aluminum can bodies frequently caused significant leaching of metals from the cupping dies, and corrosion, pitting and other damage to the cupping dies, strippers and other exposed surfaces of the press. The premature replacement of that equipment and tooling often resulted in the need for considerable additional investments which could be avoided through use of alternative xe2x80x9cneatxe2x80x9d lubricant compositions. In addition, in those systems, it is necessary to add filters to remove fines of aluminum, dirt, grits etc. from aqueous lubricant and to use emulsions, algicides and bactericides to limit the growth of microorganisms in the emulsion.
Another attempt to address the cost efficient and consistent application of liquid lubricating compositions to aluminum beverage can sheet stock is disclosed in Hahn et al., U.S. Pat. No. 5,549,752, issued on Aug. 27, 1996 to Coors Brewing Co. In that apparatus, a multi-part, reciprocating piston system was used to dispense xe2x80x9ccuppingxe2x80x9d lubricant through bores to a wick. The aluminum sheet surfaces were contacted by a wick or by a transfer roller which was in contact with the wick to apply a lubricating composition to aluminum sheet surfaces. In such systems, it was possible to use xe2x80x9cneatxe2x80x9d lubricants.
Piston controlled systems such as those disclosed in the Hahn et al. patent are relatively complex to operate and maintain which results in undesirable operational problems and increased upkeep expenses. They also often require complex electronic or other controls to avoid undesirable fluctuations in the application of lubricant compositions to the sheet surfaces, particularly when there are stock sheet feed fluctuations and temporary line shut downs. The demands on the pumps in such systems also reduced pump life further increasing the system""s operational expenses.
Systems such as that disclosed in Hahn et al., in addition, often cannot reliably and consistently maintain the required flow of active xe2x80x9cneatxe2x80x9d lubricant compositions to sheet surfaces to form the desired lubricant coatings at relatively high sheet feed rates, such as those used to maintain a xe2x80x9ccuppingxe2x80x9d press speeds of about 120 strokes per minute and greater. As a result, those systems often cannot provide the minimum amounts of lubricant required for forming aluminum xe2x80x9ccupsxe2x80x9d or other types of pressed metal objects. This limitation can be a significant impediment in aluminum can body plants which often run at an approximate average rate of about 180 xe2x80x9ccuppingxe2x80x9d press strokes per minute, and as fast as about 200-225 press strokes per minute.
The lubrication system of the invention provides an improved apparatus and method for applying one or more lubricating compositions to the surfaces of metallic sheet materials. It provides an effective, flexible and costs effective approach to forming such coating that may be used to dispense relatively small amounts of such lubricants, including xe2x80x9cneatxe2x80x9d lubricant compositions. As a result, it avoids many of the problems of the prior systems and allows significant potential cost reductions in both equipment and the use of lubricant compositions.
The invention provides an apparatus and method for applying a liquid lubricant to at least one surface of a moving metal sheet. The apparatus includes a wick and a liquid lubricant reservoir and at least one conduit in flow communication with the wick and reservoir. The liquid lubricant moves from the reservoir in controlled amounts, through the conduit or conduits to the wick by gravity flow and is moved by capillary action through the wick to the surface of the moving metal sheet without the application of an external mechanical force, such as a piston, to generate a pressure gradient through the wick to move the liquid lubricant therethrough.
The reliance upon a wicking or capillary flow for transmitting the liquid lubricant through the wick without the necessity of the application of an external mechanical force to generate a pressure gradient through the wick is extremely beneficial to simplify the apparatus applying lubricant to the metal sheet. It has been found that the capillary action by which the liquid lubricant flows through the solid but porous wick because of the relative attraction of the liquid lubricant molecules of the lubricant with the solid wick is sufficient for applying precise amount of thin lubricant coating on metal surfaces traveling at very high speeds. This simplification not only reduces the cost of the apparatus, but also lowers the risk of down time and reduces the maintenance expenses which result from more complicated and difficult to maintain mechanical lubricant application systems.
Moreover, the apparatus and method of the invention surprisingly provide an effective, sufficiently uniform lubricant coating for the purposes of press forming, drawing and ironing or other shaping of the metal sheet material. The capillary flow of liquid lubricant, which is not in the form of an emulsion, to the moving metal sheet permits a level of control of coating thickness and lubricant weight and distribution, even at relatively low coating weights, under a wide range of sheet feed rates, sheet feed rates that are highly variable during production runs, and conditions not available using conventional systems.
As a result, the invention permits the application of thin lubricant coating in manufacturing processes, such as those used to produce xe2x80x9ccupsxe2x80x9d for aluminum can bodies, without the need for aqueous lubricant emulsions or other lubricant compositions that may cause corrosion or increased wear to forming equipment, additional additives or treatment systems, or additional systems required for the preparation and dispensing of lubricant emulsions. Because the invention does not require complicated controls to generate a pressure on the lubricant to force it into and through the wick, such as a pump, piston or other similar mechanical control system, it is easily maintained and relatively inexpensive to produce. These benefits render the apparatus and method of the invention significantly more cost effective and desirable for many different applications.
In one aspect, the wick is immediately adjacent to and in contact with the moving metal sheet for application of the lubricant. In an important aspect, the reservoir is located relative to a plurality of conduits between the reservoir and wick and is located relative the wick, such that the lubricant moves by gravity from the reservoir to and through the conduits to the wick. In one aspect, the reservoir includes ports which control flow of lubricant from the reservoir to the wick, and also may control the reservoir level and amount. The conduits also may include one or more surfaces positioned to direct and spread the lubricant flow between the reservoir and wick to evenly distribute lubricant to the wick material and to avoid under supply or substantial drying of portions of the wick material.
In another important aspect the wick is immediately adjacent to and in contacting engagement with a lubricant application/transfer roller which is in rolling contact with the moving metal sheet to transfer the liquid lubricant from the wick to the moving sheet. The use of the application/transfer roller in combination with the wick which moves the liquid lubricant by capillary action and the above-mentioned controlled flow of lubricant from the reservoir is particularly effective for metering and applying precise amounts of lubricant to form a relatively thin lubricant layer on the moving sheet. Moreover, with the slowing of the metal sheet or even to the extent of stopping the sheet or equipment, the roller in contact with the wick will stop the flow of lubricant and will not cause an over abundance of lubricant on the surface of the application/transfer roller or sheet once the sheet or equipment increase speed of movement.
In another important aspect, the wick is a fibrous, felt material with properties which are effective for moving the lubricant by capillary action through the wick to another surface in contact with the wick such that at least about 130 mg/M2 of lubricant is applied to a metal sheet moving at speeds of from about 5 inches (12.7 cm) to about 90 ft. (27.4 m) per minute. The composition, density, thickness of the wick affect the capillary flow of lubricant through the wick. Each of these properties are selected to be effective for providing a metered, capillary flow of the liquid lubricant to the surface in contact with the wick to receive a coating of lubricant.
In an important aspect, the wick is made of a matrix of fibrous elements including polyester fibers, such as Dacron or a blend of polyester fibers and wool fibers with density of from about 0.072 oz/in3 to about 0.175 oz/in3. In one aspect of the wicking materials, the wick has a thickness of about 0.375 inches (9.5 mm) and a weight in the range of from about 35 oz/yd2 to about 85 oz/yd2. In another aspect, the wicking material has a thickness of about 0.75 inches (19.0 mm) and a weight of about 112 oz/yd2 which, on a unit weight basis, is similar to a wicking with a thickness of 0.375 inches (9.5 mm) and a weight of 56 oz/yd2. These wicking materials are used with liquid lubricants for forming aluminum xe2x80x9ccupsxe2x80x9d for beverage can bodies with viscosities in the range of about 40 to about 800 SSU, and preferably in the range of about 100 to about 250 SSU at about 100xc2x0 F. (37.8xc2x0 C.).
The rate at which the lubricant is applied is a function of the lubricant""s capillary flow properties under the expected operating conditions and the capillary flow provided by the wick material for the lubricant. Using the wicks with the properties described above, flow rates between the reservoir to the wick of from about 0.30 to about 2.0 ml per running foot for aluminum sheet stock about 60 in. (152 cm) wide will provide the desired amount of lubricant in an aluminum cupping process in the manufacture of drawn aluminum cans. The lubricant used in the invention is not in the form of typical aqueous emulsions which often will separate while flowing through the wick material, (e.g., in the invention, typical aluminum can cupping lubricants should not have more than about 10 weight percent water). In one important aspect, the invention permits the application of a lubricant coating of an approximately 100% active or xe2x80x9cneatxe2x80x9d lubricant coating on the surface of aluminum sheet stock moving at the above described speeds averaging from about 5 in. (12.7 cm) to about 90 ft. (27.4 m) per minute at lubricant weights as low as 130-140 mg/M2 and 20-28 mg/cup (where approximately 4 to 5 cups are formed per square foot of sheet stock), and about 2 to about 3 mg/gm of xe2x80x9ccup,xe2x80x9d using lubricant compositions with viscosities of from about 100 to about 450 Saybolt Seconds Universal (SSU) at 100xc2x0 F. (37.8xc2x0 C.), as noted above.